The invention relates to an electronic telephone switching system having peripheral units such as a plurality of subscriber and line circuits, a plurality of trunk and tie line circuits, at least one attendant line circuit, a plurality of signaling tone receivers, and a plurality of link control circuits. The system includes a one wire switching speech path matrix, a one wire switching tone matrix, and a system clock unit, including a common control comprising a program memory, a scratch pad memory, a customer memory and a central processing unit and further including, as well, incoming and outgoing information and commands as addresses between the different units of the common control unit and the different peripheral units information carrying bus lines, whereby said bus lines for changing of information in the common control carry information with faster rise time pulses than the peripheral units with the common control unit, wherefore a peripheral interface logic divides the faster bus lines from the slower peripheral bus lines.
U.S. Pat. Nos. 3,904,831 and 3,943,297 describe a private automatic branch exchange (PABX) wherein subscriber line circuits signaling receivers, signaling transmitters and connecting sets of attendant stations or consoles and other special junctors are connected as input and output units to the horizontal lines of a switching matrix. Feeding sets, internal junctors or internal feeding sets, as the case may be, are connected to the vertical lines of the switching matrix. A connection between subscriber stations connected to the rows and other input and output units is established by operating the crosspoints at two matrix crossings. As an example, the connection of a subscriber station to a junctor circuit is established by closing the crosspoint switch at only one crosspoint of the switching matrix. The number of crosspoints is dependent on the number of wires to be switched.
Techniques for establishing connections between input/output (I/O) devices connected to the horizontal lines of the switching matrix by using a switching matrix having one or more stages and by through-connecting more than one crosspoint are exemplified by U.S. Pat. No. 3,308,242 and British Pat. No. 1,058,893. The latter shows that this form of connection may also be established by wires of a single switching stage of the switching matrix, each of which connects at least two crosspoints. In this regard, reference is made to the article, "Le nouveau system telephonique Trachsel-Gfeller a reflecteurs crossbars" in the Swiss publication TECHNIQUE PTT, 1955, No. 3, pp. 115-129, and to "Der X/53er-Schweizer Kreuzschienen Hausautomat" published in HASLER-MITTEILUNGER OF HASLER AG, Bern, No. 3, 1957, pp. 57-67, as well as to U.S. Pat. No. 2,955,165. Various types of systems are employed in these known telephone systems, i.e., both directly controlled systems and those using common-control equipment.
In some of the aforementioned facilities, subscriber stations, as well as junctor and feeding circuits are to be scanned in successive cycles in accordance with the last-look principle. For example, it is known from U.S. Pat. Nos. 3,904,831 and 3,943,297, when a subscriber originates a call which is to be identified during the scanning cycle, after assignment of a junctor and feeding circuit, to commence the further states of operation, such as transmission of the selection signals, during the scanning cycle of the relevant junctor and feeding circuit in use. This means that the scan period of a junctor and feeding circuit must be comparatively long so as to be able to perform all the functions involved in the exchange of information between the junctor and feeding circuit and the connected calling and called peripheral units, such as subscriber stations.
The transmission of signal tones (e.g., dial tone, busy tone or ringback signal) to the peripheral units, such as subscriber stations, is also accomplished during the scan period of the junctor and feeding circuit being used for the connection in question. The appropriate tone is connected by linking the tone generator via appropriate tone crosspoints to a junctor circuit repeater. Hence, tone-connection and speech path crosspoints are provided. This prior art arrangement is exemplified by West German Auslegeschriften Nos. 1,079,685 and 2,111,787.
West German Auslegeschrift No. 1,079,685 describes a method of using a central zone generator whose tone signals are connected via tone-connecting crosspoints to a subscriber station; the tone-connecting crosspoints are opened and closed in synchronism with the system clock-pulse pattern for the tone (e.g., busy tone) to be transmitted. It can also be seen from West German Pat. No. 2,111,787 (VPA 71/6033, filed Mar. 11, 1971) that the tone signal is connected via a tone connection separated from the speech path connection to a repeater winding of the junctor and feeding circuit. In this patent, it is pointed out that the control circuit for the crosspoints of the tone connection is separated from the access circuit of the tone signal. It is likewise known in the time division multiplex (TDM) switching art to connect the tone during the sampling period for the junctor and feeding circuit.
The principal disadvantages of the known arrangements, such as those described in U.S. Pat. Nos. 3,904,831 and 3,943,297, are as follows:
a. Greater complexity as a result of the two-wire switching in the switching network, particularly with regard to switching control, and supervisory means as well as greater complexity of I/O units and junctor and feeding circuits.
b. Since each sampling of peripheral units occurs only during the normal periodic sequence of the scanning cycle, either the quantity of information to be exchanged during each scan or the number of I/O devices that can be connected, as well as of the junctor and feeding circuits, is considerably reduced because of the long period required for scanning these circuits.
c. Considerable technical effort is needed to permit the exchange of information, via the junctor and feeding circuits, with the units connected thereto while they are being scanned.
d. This is all the more difficult, since access is possible only via the switching matrix by scanning the horizontal lines of the switching matrix.
e. Since tone connection via the tone switching matrix is likewise a function of the scan period of the junctor and feeding circuits, this means an additional load for the outlay required for establishing the connection during the scan period of a junctor and feeding circuit.
It is an object of the invention to provide in systems such as those discussed above, a simple way to control the speech path attenuation from the common control unit, particularly in the case of single-wire speech path switching with a thyristor-type crosspoint switch.